Proper way to vent a 68 chevelle fuel tank?

[fultz1275]

Can someone tell me the proper way to vent a fuel tank on a 68 chevelle so that it doesn't puke fuel and doesn't have the strong fuel smell in the garage. Also what exactly does this plastic peice do? Does it just combine the two vent tubes into one or does it actually act as a check valve of some sort. Any help is appreciated.